The 60-W TV

Paul Wilmarth, Director, Consumer Segment Marketing, ams


Cost-neutral adaptive backlight control improves energy efficiency

Figure 1: The local-dimming function saves 10 to 20% of power on edge-lit systems (left) and 20 to 30% of power on direct back-lit TVs (right).

TVs in households are regular companions for many people around the world. It is common that people have the TV on in a living room while preparing a meal in the kitchen. In many cases, the TV is not being watched but only heard. With an average usage of four to five hours per day, every day, the TV is one of the biggest consumers of power in a household. Almost every household has a TV; some have as many as five large-format TVs. The ubiquity of the TV in every home led the CEC (California Energy Commission) in 2009 to craft aggressive power-saving goals for companies selling TVs in that state. These were the nation's first energy-efficiency standards for televisions and they mandated that new TVs with 58-inch or smaller screens sold in California should consume 33% less electricity by 2011 and 49% less electricity by 2013. While aggressive, the goals were achievable with available electronics technologies. The move from CCFL to LED backlighting and the incorporation of ambient-light sensors are rapidly enabling even more drastic power savings at leading TV manufacturers. Today over half of the TVs for sale are back lit by LEDs and most have analog or digital sensors on board to adjust the backlight in a way that maintains picture quality while saving power in low ambient-light conditions. Just as the CEC had influenced technology design in California, the U.S. Environmental Protection Agency and the U.S. Department of Energy's ENERGY STAR program did the same at a national level. While consumers are familiar with the blue and white ENERGY STAR label, few know what it actually means and both manufacturers and retailers had been lax in this area. Initial ENERGY STAR guidelines were not very affective, only measuring power usage at 0 Lux (no ambient light) and 300 Lux (room with sunlight). Taking only two measurements on the light power curve allowed manufacturers to easily earn an ENERGY STAR rating by having an unusably dim screen at 0 Lux and a full bright screen at 300 Lux. Manufacturers would adopt a simple photo diode technology, creating the appearance that they could pass these unsophisticated measurements. However, since that time, the standards have become increasingly stringent, with a new level of performance required about every 18 months. One of the first design changes that TV OEMs made in response to new ENERGY STAR guidelines was the incorporation of light sensors. With the introduction of ENERGY STAR 6.0 in the Spring of 2013, the requirements become even more challenging. For example version 6.0 calls for a 42" TV to consume just 62.8 W, and the maximum power any TV can consume—regardless of screen size—is 85 W. Measurement of power use is more thorough too. Version 6.0.requires measurement at four levels: 10, 100, 150, and 300 Lux. (Evidence suggests that more than 75% percent of people watch TV in a room with ambient light less than 50 Lux.) Analog photodiodes respond to IR energy present in the ambient light. Digital methods eliminate IR energy from the ambient-light calculation resulting in more-accurate readings at low light levels. TV OEMs will need to adopt such technology to accurately assess the light environment, communicate the environment to the processor, and adjust the backlight for optimal power savings and viewing experience for the customer. Today, commercially available technology for sensor-driven LED Lighting allows 46-inch-class TVs to consume just 60 W. Achieving this low dissipation requires TV OEMs to adopt three technologies: Local dimming, high-accuracy LED drivers, and intelligent digital light sensors. The TV Chip must support local dimming. This function looks at the video content and decides which LEDs it can dim to save power in the display. This scalar then uses the LED drivers to reduce light in those columns, for edge lighting, or sectors, in the case of direct lighting. This local-dimming function alone saves 10 to 20% of power on edge-lit systems and 20 to 30% of power on direct back-lit systems (Figure 1). Additionally, when we combine a smart digital light sensor with local dimming we realize an additional 20 to 30% power savings. The digital ambient light sensor looks at the ambient light level in the room (remember 75% of people watch TV in a dimly lit room) and adjusts the backlight to a lower power level. The impact of this is threefold, the TV has improved contrast ratio, which is noticeable and pleasing to the eye; there is no blinding or discomfort to the consumer by the overdriven display and substantial power savings is realized. OEMs can realize this additional power savings outside the HDTV chip or incorporate it into the TV-system software for additional cost savings. Note that one of the biggest power users in consumer electronics today is the flat panel TV. Current estimates attribute 3 to 4% of global residential electricity consumption to TVs—about 168 TWh, representing roughly 27 megatonnes of CO2 emissions in 2010. By 2015, efficiencies such as those described here can result in annual electricity savings of approximately 3.2 TWh, the equivalent of 1.2 megatonnes of CO2. Power-saving initiatives are not just in the US but global. The EU has adopted an energy-class system where products are ranked by power consumption: A+++, A++, A+, A, B, C or D. Most TVs today rank as an A, B, or C. By adopting sensor-driven LED backlight with local dimming, European manufacturers will be able to achieve the higher A rankings. China is also promoting energy conservation in new TV designs. Manufacturers can meet the majority of the Chinese guidelines by switching to LED backlighting. Manufacturers that export, however, will need to adopt the sensor-driven approach to have products marketable in the US and EU. There is no cost penalty to manufacturers or consumers to adopt these sensor-driven lighting technologies. They already buy components for driving LED backlighting; they already have sensors in the TV. It is simply a matter of connecting these devices in an intelligent way to optimize the design. A recent study in North America shows that when it comes to TVs, there are two items at the top of consumers' wish lists: A low power HDTV design and better picture quality. Adopting the 60-W-TV approach delivers on both of these desires and it does so without increasing the TV price in the least. ams